The long-term goal of this proposal is to elucidate the role and mechanisms of class I histone deacetylases (HDACs) in renal fibrosis. Chronic kidney disease (CKD) leading to end-stage kidney failure is associated with interstitial renal fibrosis regardless of the underlying cause. So far, there are no specific clinical treatments to target fibrosis. Renal fibrosis is characterized by aberrant activation and growth of renal interstitial fibroblasts. The activated fibroblast has been termed a myofibroblast and is defined by phenotypic changes such as the expression of -smooth muscle actin (-SMA). As myofibroblasts are able to proliferate rapidly and produce excessive matrix proteins (i.e. fibronectin) that contribute to the pathology of renal fibrosis, an approach that inhibits renal fibroblast activation and proliferation may attenuate or halt the progression of CKD. Our preliminary data demonstrate that: 1) treatment with trichostatin A (TSA), a specific inhibitor of class I/II histone deacetylases (HDACs), inhibits cell proliferation and expression of -SMA and fibronectin in cultured rat renal interstitial fibroblasts (NRK-49F) and in the fibrotic kidney induced by unilateralureteral obstruction (UUO) injury; 2) Proliferation and activation of renal interstitial fibroblasts are accompanied by phosphorylation of signal transducer and activator of transcription 3 (STAT3); 3) Blockade of the STAT3 pathway also inhibits activation and proliferation of NRK-49F; and 4) TSA abolishes STAT3 phosphorylation in NRK-49F and in the kidney following obstructive injury. From these data, we hypothesize that HDACs-mediated activation of STAT3 regulates activation and proliferation of renal interstitial fibroblasts and progression of renal fibrosis. Specific Aim1 will define the role of the class I HDAC isoforms in regulating cell proliferation and activation and global protein expression and lysine acetylation in renal interstitial fibroblasts. Specific Aim 2 will elucidate the mechanism of class I HDAC-mediated activation of STAT3 in renal interstitial fibroblasts. Specific Aim 3 will evaluate the therapeutic effect of class I HDAC and STAT3 inhibitors on the progression of renal fibrosis following obstructive injury. Successful completion of these studies will increase our knowledge of the mechanisms of renal fibrosis and facilitate the development of HDAC inhibitors as novel treatments for CKD. PUBLIC HEALTH RELEVANCE: Renal tubulointerstitial fibrosis is characterized by aberrant activation and growth of the renal fibroblasts. As histone deacetylase (HDAC) inhibitors are being investigated as potential anticancer drugs, elucidation of the functional role and mechanism of HDACs in the activation and proliferation of renal interstitial fibroblasts could lead to use of HDAC inhibitors as therapeutic agents for chronic kidney disease.